Under an open oxygen atmosphere, 1,2-phenylenediamine (1.0 mmol) was dissolved with hexanal (1.2 mmol) in ethanol (3 mL), followed by the addition of 10 mol% of catalyst. The reaction mixture was stirred at room temperature until the reaction was complete (see Table 2 for reaction times). The reaction progress was monitored by thin layer chromatography (TLC). Upon completion of the reaction, the reaction mixture was diluted with ethanol (20 mL) and the catalyst was removed by filtration. Subsequently, the organic layer was concentrated under reduced pressure and the crude product obtained was purified by silica gel column chromatography with the eluent being a solvent mixture of ethyl acetate and n-hexane (1:9, v/v), resulting in pure 2-pentyl-1H-benzo[d]imidazole. The spectral data of the product were in agreement with those reported in the literature [48], [54] and [55].
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